Hybrid vehicles may include regenerative braking and friction braking to stop a vehicle. During regenerative braking, the vehicle's kinetic energy is converted into electrical energy and stored for later use. On the other hand, friction braking converts the vehicle's kinetic energy into heat which is dissipated and lost to the surrounding atmosphere. Thus, it may be beneficial to operate with regenerative braking when braking is requested. Nevertheless, it is not always possible to operate with regenerative braking since a vehicle has limited electrical storage capacity. Therefore, there may be times when it is desirable to transition from regenerative braking to friction braking. However, a driver may notice when the vehicle transitions from regenerative braking to friction braking if the vehicle accelerates or decelerates during the transition.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for vehicle braking, comprising: providing driveline braking torque to a vehicle without applying friction braking torque to the vehicle; and reducing driveline braking torque while increasing friction braking torque to the vehicle in response to an energy storage device state of charge, the friction braking torque increased by a same amount the driveline braking torque is reduced.
By increasing friction brake torque by a same amount regenerative braking is reduced, it may be possible to transition between braking modes without disturbing the driver. For example, if regenerative braking is reducing braking torque by 2 N-m per second, friction braking may be increased by 2 N-m per second so that the friction brake torque provides the braking torque that is being reduced by the driveline. Consequently, the friction brakes counteract the decrease in driveline braking. In this way, it may be possible to transition between braking modes without disturbing a driver.
The present description may provide several advantages. Specifically, the approach may reduce braking disturbances. Further, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.